1. Field of the Invention
The present invention relates to slurry compositions, to methods of preparing the slurry compositions, and to methods of polishing an object using slurry compositions. The slurry compositions and methods may be utilized in the fabrication of semiconductor devices.
2. Description of the Related Art
Chemical mechanical polishing (CMP) is commonly utilized to planarize layers, such as metal layers, during the fabrication of semiconductor devices. CMP processes are generally characterized by rotating a pad relative to the surface of a wafer with a slurry composition interposed there between. Chemical reaction between the slurry composition and materials of the wafer, coupled with mechanical polishing, result in the smoothing (planarizing) of surface features of one or more layers on the wafer.
However, conventional slurry compositions generally suffer from a number of drawbacks. For example, an oxide layer may be undesirably eroded as the result of differing polishing rates among various layers of the wafer, such as metal layers, barrier layers, insulating layers, and so on. Also, it is known to add an oxidizing agent to the slurry composition in order to increase the polishing rate. Unfortunately, the oxidizing agent can corrode the metal layer being polished, resulting in electrical disconnects with later formed metal layers. The result is often operational failure of the semiconductor device being fabricated.
Examples of CMP slurry compositions are presented in U.S. Pat. No. 5,980,775, issued to Grumbine et al., and U.S. Pat. No. 5,958,288, issued to Mueller et al. Generally, these slurry compositions include peroxide as the oxidizing agent, and a metal catalyst for improving the oxidizing activity of the oxidizing agent in an effort to increase the polishing rate. Other examples are presented in U.S. Pat. No. 5,340,370, issued to Cadien et al., and U.S. Pat. No. 5,527,423, issued to Neville et al. These CMP slurry compositions generally include an unusually high amount of oxidizing agent in an effort to obtain a high polishing speed.
However, as suggest previously, the high concentration of oxidizing agent can cause problems. This is particularly true in the case of a metal layer, which can be etched and damaged by the conventional slurry composition. Further, voids can be disadvantageously formed in metal plugs by the oxidizing agent of conventional slurry compositions.
FIGS. 1 and 2 are SEM images showing examples of damage to a metal layer that can result from a CMP process using a conventional slurry composition. In particular, FIG. 1 is a SEM image showing the metal layer damage that can be generated in the metal CMP process using a conventional SS W2000 slurry (trade name manufactured by Microelectronics Co., U.S.A, and FIG. 2 is a SEM picture showing the metal layer damage that can be generated in the metal CMP process using a conventional W slurry (trade name manufactured by Ceil Industries Inc., Korea).
Referring to FIG. 1, when the metal layer is polished to form a metal plug using the SS W2000 slurry, voids having diameters of about 900 Å are observed at an upper portion of the metal layer. Referring to FIG. 2, when the metal layer is polished to form a metal plug using the W slurry, voids having diameters of about 600 Å are observed at the upper portion of the metal layer. The presence of such voids increases the electrical resistance of the metal plugs, thus potentially causing operational failures.
In addition, in order to polish the metal layer with a constant polishing rate, it is desirable to maintain a constant concentration of the oxidizing agent. However, the oxidizing agent (such as a peroxide compound) generally included in a conventional slurry composition is easily decomposed in water, resulting in a varying concentration of the oxidizing agent. Thus, the metal layer is not be polished at a constant polishing rate, and furthermore, the polishing rate is reduced as the polishing process proceeds.